Direct-current amplifier



Jan. 18, 1949. F. L. MOSELEY ET AL 2,459,177

DIRECT CURRENT AMPLIFIER Filed March 5, 1945' 2 Sheets-Sheet 1 VWv N Q EII Q q k x;

I IN V EN TOR.

lam/m- 1. Maxim By [law ASP/Z: Q QM Jan. 18, 1949. F. L. MOSELEY ET A].

DIRECT CURRENT AMPLIFIER Filed March 5, 1945 2 Sheets-Sheet 2 Kill I]IIIIIII Patented Jan. 18, 1949 DIRECTrCURRENT AMPLIFIER FrancisL.Moseley, Osborn, and. Lloyd J'. Perper,

Dayton, Ohio Application March 5,- 1945,.Seriai No. 581,018

(Granted. under the act of'March 3, 18.83., as

2 Claims.

The invention described herein may be manufactured and used by or fortheGovernment-f'or governmental purposes, without the payment to 1150iany royalty thereon.

The present invention relatesto. D. C. ampli-- fiers, and isparticularly usefuliin. amplifying a low direct current voltage of lowpower to one of high power.

An object of the invention is to invert weak direct current, amplify theresultant 'A. 0., and

then rectify this A. C. to a resultant direct current of greater powerto actuate controls, indicators or any mechanical or electrical. devicerequiring more voltage or power than wasavailable in the original input.

A further object is to provide such an amplifier which will utilizesimple components, be inexpensiveto manufacture and adaptable to massproduction technique.

A still further object is to'provide such an amplifier which will haveautomatic gain stability as well as centering stability'so that spuriousoutput without input is eliminated.

Another object is to provide such an amplifier which is free from groundconnections-so as to be easily adaptable to all types-f circuits Whereamplification of D. C. is desired, particularly in airborne recordingand control applications where the 28 volt battery voltage may be usedwithout special regulation 01' step-up to a higher voltage for the platecircuits.

These and other objects willappear throughout the. specification andwill be vvparticularly pointed out in the claims.

Referring to the drawings. wherein like numerals denote like parts,

Fig. lis aschematic diagramyof thev circuit I employedin the amplifier;and,

Fig. 2 is a block diagram illustrating the func reedifor. rectification.Negative.ieedbaclt.isremp amended 30, 1928; 370 0. G. 757) ployed in thevarious stages of the amplifier to maintaingain stability.

The amplifier isparticularly adaptable to the extremely low poweroutputs of. aircraft instruments, receivers and controls. For instance,it has proved effective when used with a crosspointer instrument landingindicator, the full scale'output voltage of which is of the order of 150millivolts. This voltage after amplification to 2 volts in the presentamplifier was applied. to operate the stylus of a graphic recorder. Inanother application the' same voltage of the'crosspointer landingindicator after amplification is used to actuate automaticlpilotcontrols and re-- lays for automatically flying and landingaircrafts.

The amplifier may be employed ina wide range of" power applications andfor many other purposes than herein disclosed and it is understoodtherefore thatno limitation. in the embodiment or details of thedisclosure is intended other than ascontained in the claims appendedhereto. By way of illustration, to describe an embodiment of theinvention, the D. C.v input is first filtered through a filter networkto remove any undesir able A. C. ripple and thev input is controlledthrough a series step attenuator in the incrementsdesired. The desiredamount of input resistors are also included to'avoid loading the lineand any reductionin. gain therefrom may be compensated by additionalamplification.

The: amplifierpreferably. shown includes in its circuit a. transformerinput coupling and the secondaryofthis transformer is coupled to thegrid of; thefirsttube of. the amplifier, the output of which may beresistively or. capacitively coupled to: several additional amplifierstages. Degenerative-zfeed'back between amplifier stages provides a highdegree: of stability and linearity of am- 'plification.

.As-will bezobservedfroma study of. the. schematicdrawing, no balancingcircuit is included orj necessary. The zeroposition cannot beunbalancedordrift. That is, withzero input there must depend oniasteady, D. C. supply voltage, or

tube; characteristics. for. stability; and freedom 7 from drift. areemployed to minimize effects of variable ele- Both current and voltagefeed back ments which may be present. The output of the amplifier powertube is derived from the cathode circuit but could equally well be takenfrom the plate circuit.

The output vibrator forms an output switch through an outputtransformer. This arrangement permits making and breaking of the outputswitch in synchronism with the input vibrator, also acting as amake-and-break switch,,in several ways. For instance, the contacts maybemounted on the same reed so as to be synchronized mechanically, or theymay be separately mounted with their respective vibrating reedselectrically synchronized. Thus, even thoughthe 'schematic drawingdepicts the two vibrators spaced ateither end of the circuit, in actualuse it will be found highly efficient to mount the contacts on a singlevibrating reed by proper insulation, and thereby provide a compact unitemploying a single vibrator coil.

circuit, and. chokes 5i ,and52; are employed to' filter toutunwmhtedpowerv supply ripple.

Thus it is seen that considerable powermay be derived through the novelamplifierwith a very small input signal or control voltage and -withgoodlinearity characteristics wherein the voltageoutput is directlyproportional tothe volt- In the drawings, the low input D. C. voltagewhich is to be amplified is introduced from the a receiver or othersource through input terminals ill, reversing switch H and through astepped attenuator l2 to a pair of vibrator contacts I? age input. Thereis no necessity for a centering control because zero D. C. signal inputgives zero A; C. signal when inverted by the vibrator, and

must give zero signal output when rectified. This 'novel arrangement,due to its freedom from bucking and balancing tube circuits providessuch-"a degree of centering accuracy that instruments may be calibratedand voltages may be measured directly 'with gi'ull confidence, in'thewhich invert the input D. C. voltage-toA C.;

thencethrough transformer coupling 14 which is preferably center tappedto couple the pulsed. -A. C. to the first amplifier tube i5.v Any otherconventionaltype of coupling can housed in place .of transformer I l.The A. C. voltage is impressed on grid ll of tube' [5 for amplification,

and the output is successively grid-coupled to,

the succeeding stages-of amplifier tub-es l8, I9, 26 and power tube 2|.Interstagecouplingis illustratecl through capacitators 22, 23, 24 and25.

Amplifier'tubes. l8, Hi, 20, 2| are operated as Class A amplifiers andinverse feed back is em: ployed at each stage to improve linearity ofoutput. Again, this desirable feature-may be provided or omitted,depending on the degree of gain, stability, or linearity of outputrequired.

Resistors 2t, 21, 28 also form part of the interstage couplinginconventional mannen- Inverse feed back is applied to the individualstages through resistors 29, 30, 3! that is, a portionof the output oftube 18 is applied to its gridinput 32, and similarly tubes lii'and Zllfeed back a portion of their respective output to their grid input;Current feedback is provided, through cathode resistors 33, 34, 35, 36and; outputvload 42. .Gricl bias is maintainedthrough grid resistors3'5, 38, 39, 40 in conventional manner The power output of. power tube25 isshown for illustration purposes, as derived through its cathode Mand transformer 44. The filtering network such as condensers 53,- 54 andinductance may also be provided to filter out unde sired output ripple.

The-output of transformer 44 is fed to the output vibrator 45 whererectification of the A.,C.

takes place in synchronism with the input of vibrator I3, by centertapping the secondary of the output transformer M. Phasing of theamplifier is adjusted through proper values of :ca pacitanoes andresistances in the circuit so that the output A. C. to the outputcontacts in vibrator $5 is in phase with the A. C. at the input contactsof vibrator I3. Extraneous power for amplifying the low voltage isinjected into the plate circuit of the amplifier tubes through terminals45 and switch 41. The power supply feeds'the vibrator coil 48- whichactuate's'the reed Y claimed is:

accuracy of the measurements. The output may be. varied bypr'oport'ioning. the gain components so as to obtain a logarithmic orother desired type of-gain; Initial design 'ofthe components willdetermine the type .of gain. 1 a

The input circuit of thi'samplifieris completely isolated from theoutput circuit and-there is consequently no likelihood .for the outputcircuit voltage .to' float above groundat the power supply voltage leveland thereby damage circuit compo- I nents or prevent accuracy ofoperation. U

I This amplifier permits the utilization of standard localizer andglidepathradio equipment for automatically landing aircraft. In suchapplication a preferred methodis to employ la separate amplifier forthe-glide path receiver voltage source and for the localizer. receiver.voltage source. And when these units are used in -combination ,withtherate circuit systems of'landing such as are described in-copendingapplication Number 545,l73,filed July 15,1944, now abandoned, andapplication Number 542,594, filed June 28 1944, the aircraft controlscanbe made to respond to the localizer and glide path beams with afidelity that human pilots admittedly have been unable to duplicate.

Having thus described the invention, .what "is 1. An amplifier systemfor amplifying low level direct current voltages to high level directcurrent voltages, comprising a multi-stage-alternatin current tubeamplifier and biased togoper-ate as a class A amplifier, a vibratorhaving a vibrat ing reed with av pair of spaced contacts "between whichthe reed vibrates, an input circuit for said amplifier having a.transformer'whos'e-primary winding is connected across said vibratorcontacts, the reed of the vibrator being connected in series between thedirect current sourceto. be

amplified, and the electricmidpoint of said pri-' mary, winding, wherebyzeroalternating current voltage appears in the output of theainplifierwhen zero direct current voltage'is at said input,

another vibrator'having a vibrating reed a'nd a pairof spaced contactsbetween which the reed vibrates, means coup said other vibrator to theoutput of said amplifier for full waverectification, the vibratoryarmature-of the first-mentioned vibrator being conductively-isolatedfrom 5 direct current ground in the absence of direct REFERENCES CITEDcurrent input Voltages and the input terminals The following referencesare of record in the of the system and the output terminals of the ssystem being effectively isolated from each other file thls patent withrespect to the passage of direct current, 5 v UNITE!) STATES PATENTS 2.An amplifier system according to claim 1 in Number Name Date which eachstage of said muiti-tube amplifier has 1,423,156 Espenslchied Sept 51922 i plate circuit back-coupled to its grid circuit 2,114,298 Gunn Apt19' 1938 for alternating current feedback. 2,133,670 SChuchmann Oct. 18,1938 FRANCIS MOSELEY- 2,190,317 Holst Feb, 13, 194

LLOYD PERPER- 2,297,542 Eberhardt Sept. 29, 1942

